It is known that centrifuges are effective in the removal of fine solids from solution. It is also known that dilution of a supporting fluid containing fine solids with a clean supporting fluid of the same type (i.e. free of fine solids) can be used reduce the viscosity and density of the fluid and improve the operational efficiency of the centrifuge. That is, by reducing the fluid viscosity, a higher proportion of fine solids may be removed from the supporting fluid. Unfortunately, while this method may result in an increase in the total amount of solids that may be removed from the supporting solution, the increase in the remaining volume of supporting fluid may or may not be beneficial.
In the case of drilling fluids used in hydrocarbon recovery, it is desirable to remove drill cuttings and fine solids from the drilling fluid as it is returned to the surface and prior to reintroduction downhole. This is normally accomplished by a combination of equipment including shakers and centrifuges. Normally, the shaker is employed to remove larger drill cuttings over a screen whereas a centrifuge is utilized to remove fine solids. The use and operation of the centrifuge will generally be dictated by the drilling fluid chemistry where the system operators will be seeking to either return the drilling fluid to a state similar to the original fluid or be adjusting the drilling fluid chemistry based on the drilling results. In other words, a drilling fluid is designed for a particular drilling program wherein management or control of parameters such as viscosity and fluid density are very important to the success of the drilling program. As fine solids become suspended within the drilling fluid, the chemistry affecting the viscosity of the fluid may change substantially. Accordingly, surface analysis of the drilling fluid is required to determine the most effective surface treatments to adjust the drilling fluid chemistry.
As a result, and depending on the drilling fluid, the centrifuge may be operated to maximize all solids removal or alternatively balance solids removal based on other drilling fluid parameters. For example, in an unweighted fluid, it may be desired to maximize fine solids removal in the centrifuge whereas with a weighted fluid, the use of the centrifuge may be balanced against maintaining the weighting agent in the fluid. Generally, centrifuges are operated to ensure that the total concentration of drilled solids in the drilling fluid is maintained at around or below 5% by volume.
A key problem in the operation of centrifuges with drilling fluids is the effect of fluid dilution. As noted above, a centrifuge may be made to be more efficient at fine solids removal by decreasing the viscosity of the fluid through the addition of a further volume of supporting fluid. However, this will result in an overall volume increase of the fluid which may then require additional treatment to re-adjust the viscosity to a desired degree. As drilling fluids, are highly expensive, there has been a need for a system and method of enhancing the removal of fine solids from drilling solutions without permanently affecting the viscosity or volume of the drilling fluid.
More specifically, there has been a need for a system and method for temporarily reducing the viscosity and density of fluid within a centrifuge such that the operational efficiency of the centrifuge is improved.
A review of the prior art reveals that such a system has not been developed in the past.